The present invention relates generally to optically coupled communication apparatus comprising a terminal unit and station unit located remotely from one another and deals more particularly with communication apparatus utlizing baseband digitally formatted optical signals to establish a two-way optical communication link between a terminal unit and a station unit. The invention also deals specifically with communication on the public telephone network wherein a user via a remote, portable, terminal unit establishes a two-way digitally formatted optical communication link with a coin operated pay telephone instrument and the like equipped with the station unit of the invention.
Telephonic communications via the public telephone network has grown substantially over the past few years as the numbers of the traveling public become larger and as more and more people become reliant on the ability to communicate with others to gain their livelihood, such as, for example, salesmen and the like. Such communication is generally accomplished utilizing the so called pay or coin operated telephone instrument and includes credit card and the like type operated telephone instruments. In order to meet the increased demand for access to the public telephone network, the so called cellular type telephone service was introduced wherein a user is assigned a dedicated telephone number and may originate and receive telephone calls by means of a cellular type telephone instrument cooperating with a mobile radio receiver. Although cellular type telephone service permits a user to place and receive a call from any location within a cellular area from his own cellular telephone, cellular telephone instruments and cellular telephone service are relatively expensive and in some instances not available in all geographic locations. Accordingly, the majority of telephone callers still access the public telephone network via conventional coin operated, credit card and the like type telephone instruments.
Applicant's U.S. Pat. No. 4,829,561, assigned to the same assignee as the present invention and incorporated herein by reference, discloses apparatus for optically coupling a terminal unit to the public telephone network through a pay telephone instrument and the like wherein the optical communication link is established by the "brute force" transmission of baseband audio frequency signals that have been converted to an energy beam typically an infra-red optical signal. The device of the above-referenced patent utilizes baseband analog techniques and is susceptible to the limitations and problems generally associated with any device utilizing analog baseband frequency operation.
The aim therefore of the present invention is to provide communication apparatus utilizing a digital communications protocol to generate a digitally formatted optical signal to provide a two-way communication link between a terminal unit and a station unit located remotely from and in line-of-sight alignment with one another.
It is a further object of the present invention to provide a telephonic device that is portable and personal to a user and which permits access to the public telephone network while overcoming disadvantages associated with conventional coin-operated operated, credit card and the like type telephone instruments.